Earthworking machines, such as track-type tractors, are used to push and carry material over a distance as part of a material removal or shaping process. Generally, it is desired to move the earthworking machine in a relatively straight line from a start position to a desired end position. However, unequal forces exerted on the blade of the machine are caused by characteristics of the material being pushed, such as large rocks and different material types, e.g., clay, sand, and the like. These unequal forces tend to push the machine in directions other than the desired straight line, and cause the earthworking machine to deviate from the desired direction of travel. In addition, slippage of one of the tracks of the earthworking machine may cause the machine to deviate from the desired direction of travel.
In U.S. Pat. No. 5,487,428, Yamamoto et al. disclose a system which tilts the blade of a bulldozer in a manner to control steering of the bulldozer in response to determining that the yaw of the bulldozer has changed due to the bulldozer being forced off of its desired straight line of travel. However, the yaw of the machine does not indicate the desired direction of travel, and therefore the operator is responsible for determining a new desired straight line after steering compensation is made. The responsibility of ensuring that the bulldozer continues to travel the desired straight line path is left to the operator of the machine. In addition, by the time that yaw is detected, the machine may have moved a significant amount from the desired course. It would be desirable to maintain the desired straight line path of the machine in a more quickly responsive manner, and without the need for active operator intervention.
Much work has progressed toward making various functions of earthworking machines autonomous or semi-autonomous. For example, in U.S. Pat. No. 5,560,431, Stratton discloses a system which controls the depth of the blade of an earthworking machine in the material being moved to optimize the work being performed by the machine. Parameters such as ground speed, track slip, slope, angular rate, and tip position of the blade are monitored and the optimal height of the blade is then determined and attained. The invention disclosed by Stratton relieves an operator of the responsibility for continually raising and lowering the blade to achieve what is believed to be optimum machine performance. However, the operator would still have to monitor the straight line desired path of travel of the machine and make continual steering adjustments as the machine pushed material to a desired end location. A system which would make straight line steering of the machine an autonomous function, and which could work in cooperation with a blade load optimizing system such as the one disclosed by Stratton, would be a desirable addition toward an efficient autonomous or semi-autonomous earthworking machine.
The present invention is directed to overcoming one or more of the problems as set forth above.